1. Field of the Invention
The present invention relates to a high frequency receiving circuit for receiving a high frequency signal, and a receiving apparatus and a receiving system each utilizing the same high frequency receiving circuit. In particular, the present invention relates to a high frequency receiving circuit provided with a controller for turning on and off power supply to a local oscillator, and a receiving apparatus and a receiving system each utilizing the same high frequency receiving circuit.
2. Description of the Related Art
FIG. 9 is a block diagram showing a configuration of a radio receiving circuit according to a first prior art example. The radio receiving circuit shown in FIG. 9 includes an antenna 71, a high frequency amplifier 72, a frequency converter 400, a local oscillator 31, a band-pass filter 73, an intermediate frequency amplifier 74, a demodulator 75, and an output terminal 76. In this case, the frequency converter 400 includes a high frequency input terminal 10, a frequency-converted signal output terminal 11, an oscillation signal input terminal 12, and a mixer 20.
Referring to FIG. 9, a radio signal having a radio frequency fRF transmitted from a transmitter apparatus is received by the antenna 71, and then, the received radio signal is amplified with low noise by the high frequency amplifier 72. The low-noise amplified radio signal (referred to as a high frequency signal hereinafter) is inputted to a first input terminal of the mixer 20 through the high frequency signal input terminal 10. In addition, a local oscillation signal having a local oscillation frequency fLO generated by the local oscillator 31 is inputted to a second input terminal of the mixer 20 through the oscillation signal input terminal 12. The mixer 20 multiplies the high frequency signal inputted to the first input terminal by the local oscillation signal inputted to the second input terminal to generate a frequency-converted signal of a multiplied result which is frequency-converted, and outputs the same frequency-converted signal to the band-pass filter 73 through the frequency-converted signal output terminal 11. Then, the band-pass filter 73 band-pass-filters an intermediate frequency signal having a predetermined intermediate frequency fIF from the frequency-converted signal, and outputs the intermediate frequency signal to the demodulator 75 thorough the intermediate frequency amplifier 74. Further, the demodulator 75 demodulates the inputted intermediate frequency signal into a base band signal using a predetermined demodulating method, and outputs the base band signal to an external apparatus through the output terminal 76.
In the prior art example, in many cases, the frequency converter 400 is constituted by a semiconductor integrated circuit, and the local oscillator 31 is constituted by a resonance circuit including a transistor, an inductor, a capacitor and the like. However, only the transistor is incorporated in the semiconductor integrated circuit in some cases. In this case, the intermediate frequency fIF of the intermediate frequency signal is represented by the following equation (1) with the radio frequency fRF of the radio signal and the local oscillation frequency fLO of the local oscillation signal:fIF=|fRF±fLO  (1).
In general, the frequency converter 400 converts the radio signal having the higher radio frequency fRF into the intermediate frequency signal having the lower intermediate frequency fIF, and the intermediate frequency signal having the lower intermediate frequency fIF is demodulated by the demodulator 75.
FIG. 10 is a block diagram showing a radio receiving circuit according to a second prior art example. The radio receiving circuit of FIG. 10 is characterized by including a frequency converter 500 incorporating a local oscillator 30 instead of the frequency converter 400 as compared with the radio receiving circuit of FIG. 9. Referring to FIG. 10, the local oscillator 30 includes a transistor and a resonance circuit, and the frequency converter 500 does not have a local oscillation signal input terminal 12. In addition, when an inductor and a capacitor of the resonance circuit used in the local oscillator 30 of the frequency converter 500 are provided on the semiconductor integrated circuit, a small frequency converter can be provided.
FIG. 11 is a block diagram showing a configuration of a diversity radio receiving apparatus according to a third prior art example. The diversity radio receiving apparatus of FIG. 11 has radio receiving apparatuses of two systems shown in FIG. 9, and the diversity radio receiving apparatus is characterized by further including a switch 77 and a diversity controller 80 as compared with the radio receiving apparatus of FIG. 9. The radio receiving apparatus of the second system is provided with an antenna 71a, a high frequency amplifier 72a, a frequency converter 400a, a band-pass filter 73a, an intermediate frequency amplifier 74a, and a demodulator 75a, and is constituted in a manner similar to that of the radio receiving apparatus of FIG. 9. In this case, an antenna 71 and the antenna 71a are provided at different positions. In addition, the frequency converter 400a is provided with a high frequency input terminal 10a, a frequency-converted signal output terminal 11a, an oscillation signal input terminal 12a, and a mixer 20a, and the frequency converter 400a is constituted in a manner similar to that of the frequency converter 400.
A local oscillation signal generated by the local oscillator 31 is inputted to a mixer 20 through a local oscillation signal input terminal 12, and is inputted to the mixer 20a through the local oscillation signal input terminal 12a. In addition, a demodulated base band signal outputted from a demodulator 75 is outputted to an output terminal 76 through a contact “a” of the switch 77, and a demodulated base band signal outputted from the demodulator 75a is outputted to the output terminal 76 through a contact “b” of the switch 77a. The diversity controller 80 switches over the switch 77 so as to select the base band signal having a higher signal quality, based on a signal quality such as a bit error rate of each base band signal outputted from each of the demodulators 75 and 75a. 
According to the diversity radio receiving apparatus shown in FIG. 11, high frequency signals having the same radio frequency fRF are inputted to the high frequency signal input terminals 10 and 10a of the frequency converters 400 and 400a, respectively. Since one local oscillator 31 generates local oscillation signals having the same frequency fLO and supplies them to the two local oscillators 400 and 400a, frequency-converted signals having the same frequency-converted component are outputted to the frequency-converted signal output terminals 11 and 11a of the two frequency converters 400 and 400a according to the above equation (1). In this case, the signals of the same frequency is inputted to the two high frequency signal input terminal 10 and 10a, however, since radio signals received by the antennas 71 and 71a positioned at different positions are inputted thereto, the frequency-converted signals outputted from the two frequency-converted signal output terminals 11 and 11a are different in signal state in many cases. Thus, by selecting the base band signal from the demodulator 75 or 75a corresponding to the frequency-converted signal output terminals 11 or 11a which is superior in receiving state and having a preferable signal quality (a signal level of the frequency-converted signal is higher, for example), the receiving state is remarkably improved. In addition, since the configuration of the diversity radio receiving apparatus shown in FIG. 11 is very effective at the time of moving reception, it is disclosed in the Japanese Patent Laid-open Publication No. JP-2004-147082-A, for example.
FIG. 12 is a block diagram showing a configuration of a diversity radio receiving apparatus according to a fourth prior art example. The diversity radio receiving apparatus shown in FIG. 12 is different from the diversity radio receiving apparatus shown in FIG. 11 in the following points.
(a) The frequency converter 500 shown in FIG. 10 is provided instead of the frequency converter 400 and the local oscillator 31 shown in FIG. 11.
(b) A frequency converter 500a having a configuration similar to that of the frequency converter 500 shown in FIG. 10 is provided instead of the frequency converter 400a and the local oscillator 31 shown in FIG. 11.
In this case, the frequency converter 500a is provided with a high frequency signal input terminal 10a, a frequency-converted signal output terminal 11a, a local oscillator 30a, and mixer 20a. 
According to the diversity radio receiving apparatus shown in FIG. 12 having the above configuration, its size becomes large because of provision of the frequency converters 500 and 500a. However, its size can be reduced since the frequency converters 500 and 500a incorporate the local oscillators 30 and 30a, respectively.
According to the radio receiving apparatus shown in FIG. 10, an entire size of the radio receiving apparatus including the local oscillator 30 can be reduced as compared with the radio receiving apparatus shown in FIG. 9. However, a local oscillation signal cannot be inputted from an external circuit of the frequency converter 500, and the radio receiving apparatus cannot be flexibly constituted.
In addition, according to the diversity radio receiving apparatus of FIG. 12, since the local oscillator 30 and 30a are incorporated in the respective frequency converters 500 and 500a, the frequency converters 500 and 500a requires the local oscillator 30 and 30a, respectively. In the example shown in FIG. 12, two local oscillator 30 and 30a operate. As a result, although its size can be reduced as compared with the configuration of FIG. 11, the current consumption for one local oscillator increases. In addition, the signal interference between the local oscillators 30 and 30a generates since the local oscillation signal leaks to the other frequency converter, and this leads to deterioration in the signal quality of the received radio signal.